Understanding the formation of pinholes in PFSA membranes with the essential work of fracture (EWF) E. Moukheiber, C. Bas, L. Flandin* LEPMI, UMR 5279, CNRS, Grenoble INP e Universite ´ de Savoie e Universite ´ J. Fourier, LMOPS e INES e Ba ˆ t. He ´lios, Campus de Savoie-Technolac, F-73376 Le Bourget-du Lac Cedex, France article info Article history: Received 24 January 2013 Accepted 6 March 2013 Available online 29 March 2013 Keywords: Polymer electrolyte fuel cells Reinforced composite polymer elec- trolyte membrane Nafion Ò membrane Short-side-chain perfluorosulfonic acid (SSC PFSA) membranes Long-side-chain perfluorosulfonic acid (LSC PFSA) membranes Essential work of fracture (EWF) abstract One of the most harmful degradation process in PEM fuel cell is the development of pin- holes in the membrane. There is therefore a need for an effective experimental charac- terization to allow ab initio membrane comparison. In this paper, the mechanical fracture resistance of various PFSA membranes was studied using the essential work of fracture (EWF) and tensile tests. PTFE reinforced membrane better resists pinholes formation due to its high resistance to crack initiation and propagation. Additionally, energy partitioning showed that the necking and tearing stage of the layered structure membrane accounts for the main part of the total fracture energy due to enhanced plastic deformation of PTFE. Moreover, cracks were found to initiate and propagate easily in the direction parallel to the polymer chains which suggest that the fracture control could be optimized by pointing the direction of the gas channel perpendicularly to the orientation of the polymer chains, i.e. to rolling process during manufacturing. Finally, EWF technique was found to be more rele- vant for assessing the differences in the mechanical behaviour of the membranes compared to standard tensile tests. Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction To secure long-term durability and efficiency of proton exchange membrane (PEM) for fuel cells, perfluorosulfonic acid (PFSA) based membrane must demonstrate long-term electrochemical and mechanical integrities [1e4]. One of the failure modes that limits the lifetime of the fuel cell involves the fracture of the membranes. The mechanisms of pinhole formation and subse- quent crack growth and propagation are complex and not fully understood. Nonetheless, those defects are likely to result from the combination of chemical and mechanical effects. Variations in the temperature and humidity during operation cause hy- drothermal stresses in constrained membranes and MEA [5e8].A considerable thinning of the membrane was reported under fuel cell operation or OCV due to massive ionomer loss throughout the active area caused by radical attacks [9,10]. Mud cracks of different depths, typically present in the electrodes can cause delamination and/or cracking of the PEM membranes [11]. In a recent work, SEM photomicrographs around the detected flaws revealed linear cracks in the membrane essentially oriented in the direction of the gas path which points out the sharp edges of the gas channels [12]. Platinum catalyst dissolution and recrys- tallization, cationic contaminants are also believed to contribute to the embrittlement of polymer electrolyte membranes [10]. Consequently, this can lead to reactant gases crossover, localized heating and ultimately the failure of the membrane and thereby * Corresponding author. E-mail addresses: Lionel.Flandin@univ-savoie.Fr, flandin@altern.org (L. Flandin). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 39 (2014) 2717 e2723 0360-3199/$ e see front matter Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijhydene.2013.03.031